In precision hydromechanical or electrohydraulic servovalves it is necessary to linearly reciprocate control members such as spool valves. In many instances it is necessary to mechanically couple two or more shafts together to accomplish such motion. Where the shafts are constructed of a single piece of metal or where conventional coupling devices are utilized, very strict tolerance requirements must be met in the formation of the bore receiving the valve as well as the lands upon the valve to avoid excessive operational wear, binding or the like, and a resultant reduction of the life of the valve.
As a result of the foregoing, the prior art has adopted the improvement of providing the pistons in a multiplicity of pieces which are then held together in various mechanical fashions. The best prior art known to applicant is shown in U.S. Pat. Nos. 2,742,924, 2,826,178, 2,928,380 and 3,608,586. Although the prior art operates adequately in the various applications under consideration, it has been found to be unsatisfactory in those applications where zero backlash is required.